This application is a Continuation Application of U.S. application Ser. No. 11/715,631, filed on Mar. 8, 2007, entitled: MULTI-LEVEL ELECTRICAL FUSE USING ONE PROGRAMMING DEVICE, now pending.
The present invention relates generally to an integrated circuit (IC) design, and more particularly to a system of circuit designs used for programming an electrical fuse using only one programming device, and a method for programming a multi-level electrical fuse system.
Electrical fuses are often utilized for modern semiconductors for making adjustments and repairs that are performed as late as after a semiconductor chip is packaged. They are designed to be blown when a current through the fuses exceeds a predetermined threshold, thus causing energy build-up that in turn blows the fuses. By blowing a fuse during programming, nonvolatile data storage can be provided. Electrical fuses can be flexibly positioned even in the most complex semiconductor designs, since wirings are allowed above and below the fuses, thereby making electrical fuses a desirable component for higher density memory devices.
A conventional system used for the programming of electrical fuses is designed to only program two-state fuses that can only provide one of the two states: “1” or a “0”. As such, it is difficult to achieve high data volume, such as 64 k-bits or more since there will be a very high bit count that requires a large number of electrical fuses. As the bit count reaches an even higher number, the probability that the semiconductor circuit may malfunction due to a bit malfunctioning increase, thereby reducing overall yield. To improve the efficiency of electrical fuses, multi-level electrical fuses that can be programmed into one of three states have been used recently. These multi-level electrical fuses can increase in density and can be implemented in a smaller effective area. For example, by using 10 cells, a three-state electrical fuse system can yield 3^10 or 59,049 data options, while a two-state electrical fuse system can only yield 2^10 or 1,024 data options. However, the original design for a multi-level electrical fuse circuit requires an additional programming device in order to program the multi-level fuse properly. This additional programming device is a penalty that space-conscious semiconductor designers can ill afford.
Desirable in the art of integrated circuit designs is a new multi-level electrical fuse system that achieves a higher data volume without resorting to larger bit count and increasing the number of programming devices.